Up to now, an image forming apparatus having a so-called tandem structure is proposed in which a plurality of image forming units for forming toner images of respective different colors such as cyan, magenta, and yellow are disposed in one direction for arrangement. In the above-mentioned image forming apparatus, the toner images of the respective colors are overlapped and transferred on paper conveyed in the arrangement direction of the image forming units.
Also, in the image forming apparatus of this type, because of, for example, an installment error of the image fowling units or the LED print heads in the exposure units or error of an operation of a photosensitive drum or the like due to an increase in an interior temperature generated owing to operations of the image forming unit, formation positions of the toner images of the respective colors may be mutually misregistered. As a result of this misregistration, a formation of an image having a color different from a target image, which is so-called color misregistration, occurs. Thus, an image forming apparatus provided with a function of performing a color misregistration correction processing for correcting the color misregistration has been proposed.
A technology related to the color misregistration correction processing has been proposed as follows. With an aim to avoid conducting a wasteful color misregistration correction, each pattern for a color misregistration check is formed in the image forming units of the respective colors. The pattern for the color misregistration check formed by transferring the color misregistration check patterns on an intermediate transfer belt is detected. On the basis of the detection result, a color misregistration check mode is executed for determining whether or not the color misregistration correction is to be executed in conjunction with other correction modes (e.g., image correction processing may include surface potential correction processing on an image bearing member of image forming means, highest density correction processing, and tone correction processing).
However, as the color misregistration check mode in the above-mentioned technology is a mode for causing the image forming units of the respective colors to respectively form the patterns for the color misregistration check, when a monochrome printing operation is carried out, a state is established in which the image forming operations by the image forming units of the colors except for black are prohibited, and a check on the color misregistration amount cannot be performed. Therefore, it is necessary to carry out the check on the color misregistration amount and the color misregistration correction after a situation is established in which a color printing operation is to be performed, which causes a user to wait for a relatively long time until the correction ends.
Also, a technology related to the color misregistration correction processing has been proposed as follows. When a normal state is returned from a power save mode, a fixing temperature is detected, and in a case where the fixing temperature is lower than or equal to a predetermined temperature, a first color misregistration correction is carried out. A first temperature at that time and a first color misregistration correction amount are stored in a memory. Furthermore, in a case where the fixing temperature is equal to or higher than the predetermined temperature, a second color misregistration correction is carried out, a second temperature at that time and a second color misregistration correction amount are stored in the memory. A magnitude between the fixing temperature at a subsequent time t and the second temperature is compared. In a case where the fixing temperature at the time t is higher than or equal to the second temperature, the color misregistration correction is performed by using the second color misregistration correction amount. In a case where the fixing temperature at the time t is lower than the second temperature, the color misregistration correction is performed by using the first color misregistration correction amount.
Also, according to the above-mentioned technology, in order to carry out an operation of correcting the color misregistration at the time t (hereinafter, this color misregistration correction will be referred as main correction), when the normal mode is returned from the power save mode, it is necessary to carry out the first color misregistration correction and the second color misregistration correction described above for obtaining the color misregistration correction amount eventually used for the main correction. For that reason, while the first color misregistration correction and the second color misregistration correction are carried out, a state is thereby established in which the image formation cannot be performed. Therefore, according to the above-mentioned technology, such a problem occurs that the user needs to wait for a time used for carrying out the first color misregistration correction and the second color misregistration correction described above.
Furthermore, according to the above-mentioned technology, even in a case where eventually the main correction does not need to be performed, as the first color misregistration correction and the second color misregistration correction described above for checking the necessity of the color misregistration correction are carried out, a toner consumption amount is accordingly increased as compared with a configuration where only the main correction is carried out.
In order to suppress this toner consumption amount, it is conceivable to adopt means for performing the drive of a developing device which is carried out at the time of the color misregistration correction in a state where the toner consumption is suppressed as much as possible. However, in a case where the operation of performing the drive of the developing device is repeatedly executed in a state where the toner consumption is suppressed as much as possible, substantial mechanical stress affects toner in the developing device, and such a state may be established that the toner is abnormally charged. As such, a state may be established in which an electrostatic latent image is not appropriately developed even when developing conditions such as a developing bias is adjusted in some cases.